This invention relates to methods of storing foodstuffs and apparatuses for practicing the same, and more particularly to a method of storing foods and an apparatus for practicing the same in which an electrochemical oxygen removal device including a gas diffusion electrode capable of selectively reducing oxygen in the air electrolytically employed to control the oxygen concentration in a food storage chamber to a desired value, to thereby prevent the deterioration of the quality, especially the freshness, of a food due to its breathing.
It is well known in the art that a method of cold storage or refrigeration is employed for storing or preserving foods. Furthermore, it is also well known that in the case where these methods are insufficient for storing foods, a so-called "controlled atmosphere (CA) storing method" is employed in which the environmental conditions of the food such as the temperature, humidity, oxygen concentration, carbon dioxide concentration, etc. in the storage chamber are controlled.
During the storage, foods, especially fruits or vegetables, breathe the oxygen in the storage chamber, to produce carbon dioxide and water while their freshness is degraded. If in this case the aforementioned CA storage method is employed, the oxygen concentration in the storage chamber can be maintained low. Therefore, the foods' breathing is suppressed, as a result of which the freshness is maintained for a long period of time.
With respect to the CA storage technique, a natural CA method and a mechanical CA method, or a flush type CA method, have been employed.
In the former method, a controlled atmosphere state in the storage chamber is obtained by the respiration of the food itself stored therein. In other words, if foods are stored in an extremely gastight refrigerator, the level of oxygen in the refrigerator is gradually reduced by the respiration of the foods while the level of carbon dioxide is gradually increased, as a result of which the respiration of the foods becomes gradually inactive. The advantage of this method lies in that no auxiliary means for controlling the oxygen concentration is provided, and therefore the cost for installation and operation of such an auxiliary means is zero. However, the method is still disadvantageous in that the fabricating cost of the refrigerator is very high because the airtightness of it must be very good, and it takes a long period of time (20 to 30 days) until the oxygen concentration reaches the required value, during which the foods are degraded in quality and, therefore, it is not permissible to open the door of the refrigerator for investigation and partial shipment of foods.
On the other hand, in the latter method, that is, the mechanical CA method or the flush CA method, a gas mixture low in oxygen concentration and containing carbon dioxide, which is obtained by burning a fuel mixture such as propane gas or natural gas and the air, is flushed into the refrigerator. This method is disclosed, for instance, by a publication "Food Engineering" 45(6), pages 318-319, (1964). The advantage of the method lies in that the period of time required for decreasing the oxygen concentration in the refrigerator is merely one to three days which is shorter than that in the case of the natural CA method described above, and that even a refrigerator poor in gastightness can be used. However, this method has various disadvantages. The device for providing the low oxygen concentration is considerably bulky, and intricate in construction and, therefore, it is expensive. Furthermore, as the mixture of gases is burned at high temperature, its burner's service life is relatively short. It is difficult to operate the device intermittently and to control the oxygen concentration with high accuracy. In addition, poisonous gases may be produced because of incomplete combustion.